The OP asked if it was legal. Not if it was a good idea or not. The good idea answer depends on the situation and the loads. A lot of teams have 3D printer at events. So you might be printing your unobtainium part at the event.
How long of a hex shaft can you print any way?
Depends on the printer, but I’ve seen wraparounds for hex shaft at close to a foot before.
With a belt printer, like the CR-30, you could theoretically go infinitely long… Not sure why you would, but you could. https://store.creality.com/products/cr-30-3d-printer
To Make Myself Clear, Me And My Team Bringed Up An Idea That Is a “PROTOTYPE” But It Has A Good Chance Of Begin On The Robot In The Season Itself. But It Will Only Happen After We Will Test It In Harsh Condition Like Running The Motors At Full Throttle.
The Reason For This Idea Was After We Discoverd That Our Output Hex Shafts Are Too Long For Placing a Magnet Inside of Them For An SRX Encoder, For Context: Our Magnet Were Going TROUGH the Encoder.
We could Just Drill inside The Hex To Make More Space Inside For The Magnet. With That In Mind Then We Tought, Isn`t There A Cheaper And Faster Way To Have a Perfect Hex Shaft And Not Ruining a Metal Shaft For Puting The Magnet Deeper? Also we Are Not So Financialy Stable so Getting New Shaft Would not Be That Easy And Fast Because we Are an Israeli Team.
So This shaft Will be Tested as Prototype For now And will Go In The ToughBox Of a West Coast Chassie. I Will Answer About The Results Later.
With That Also in mind, We Are Printing Out Of A Strong Plastic Filiment That Contains A Fiber In It. So The Durabiltiy Will Be Strong But We Will Announce The Result Later How I Said Previously.
Thanks For Each And Everybody Here For Helping And Debating This Post, Thanks From Bat Yam, Space Monkeys 6741!